RAF2 is a RuBisCO assembly factor in Arabidopsis thaliana

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes the reaction between gaseous carbon dioxide (CO₂) and ribulose‐1,5‐bisphosphate. Although it is one of the most studied enzymes, the assembly mechanisms of the large hexadecameric RuBisCO is still emerging. In bacteria and in the C4 plant Zea mays, a protein with distant homology to p terin‐4α‐c arbinolamine d ehydratase (PCD) has recently been shown to be involved in RuBisCO assembly. However, studies of the homologous PCD‐like protein (RAF2, RuBisCO assembly factor 2) in the C3 plant Arabidopsis thaliana (A. thaliana) have so far focused on its role in hormone and stress signaling. We investigated whether A. thalianaRAF2 is also involved in RuBisCO assembly. We localized RAF2 to the soluble chloroplast stroma and demonstrated that raf2 A. thaliana mutant plants display a severe pale green phenotype with reduced levels of stromal RuBisCO. We concluded that the RAF2 protein is probably involved in RuBisCO assembly in the C3 plant A. thaliana.     

Food provision to nestlings in the Hoopoe Upupa epops: implications for the conservation of a small endangered population in the Swiss Alps

In an attempt to recognize the possible ecological causes of the decline of a population of Hoopoes Upupa epops in the Swiss Alps, we collected data on resource exploitation. The prey provisioned to nestlings by parents was investigated at four breeding sites using photographs (n = 4353, 80% of which enabled prey identification). Molecrickets Gryllotalpa gryllotalpa and Lepidoptera (larvae and pupae) were dominant in nestling diet (93% frequency; 97% biomass). Although Molecrickets were provisioned less frequently (26%) than Lepidoptera (67%), they represented 68% of the total biomass (vs 29% for Lepidoptera). There was an overall negative relationship between the proportion of Molecricket biomass in the diet and the parents' feeding rate, whereas a comparison between broods showed that a higher provisioning activity did not lead to an increase in the biomass supplied to the chicks. A diet based on Molecrickets therefore appears to be energetically advantageous. As Molecrickets are a traditional prey of Hoopoes in central Europe, this might be relevant to other populations. In the study area, Molecrickets occur only on the intensively cultivated plain, whereas the majority of Hoopoe pairs nest at various altitudes on the foothills adjacent to the plain as the latter provides at present almost no suitable nesting sites. Hoopoes breeding higher up on the foothills seem to experience greater provisioning costs and have, on average, lower breeding success. Providing nest sites on the plain is the main conservation measure proposed for the local Hoopoe population. Further attention should also be paid to Molecrickets as these may be crucial for Hoopoes.     

How membrane proteins travel across the mitochondrial intermembrane space.

A newly discovered family of small proteins in the yeast mitochondrial intermembrane space mediates import of hydrophobic proteins from the cytoplasm into the inner membrane. Loss of one of these chaperone-like proteins from human mitochondria results in a disease that causes deafness, muscle weakness and blindness.     

Cyclic Expression of A Nuclear Protein In A Dinoflagellate

Nuclei of the dinoflagellate Crypthecodinium cohnii strain Whd were isolated and nuclear proteins were extracted in three fractions, corresponding to the increasing affinity of these proteins to genomic DNA. One fraction contained two major bands (48- and 46-kDa) and antibodies specific to this fraction revealed two major bands by Western blot on nuclear extracts, corresponding to the 46- and 48-kDa bands. The 48-kDa protein was detected in G1 phase but not in M phase cells. An expression cDNA library of C. cohnii was screened with these antibodies, and two different open reading frames were isolated. Dinoflagellate nuclear associated protein (Dinap1), one of these coding sequences, was produced in E. coli and appeared to correspond to the 48-kDa nuclear protein. No homologue of this sequence was found in the data bases, but two regions were identified, one including two putative zinc finger repeats, and one coding for two potential W/W domains. The second coding sequence showed a low similarity to non-specific sterol carrier proteins. Immunocytolocalization with specific polyclonal antibodies to recombinant Dinap1 showed that the nucleus was immunoreactive only during the G1 phase: the nucleoplasm was immunostained, while chromosome cores and nuclear envelopes were negative.     

白马雪山国家级自然保护区典型森林生态系统服务

生态系统服务是近年来生态学研究的热点领域,对关键区域生态系统服务的研究具有重要意义.云南省白马雪山国家级自然保护区地处青藏高原南延部分,拥有独特的地理位置,是生物多样性保护的热点区域.本文对该保护区森林生态系统的生物量与生产力、水源涵养、营养物质循环等3项服务的功能量进行了评估.结果表明:保护区森林总生物量2215.86×104t,生产力171.84×104t·a-1;水源涵养量11964.56×104m3;N、P、K年吸收量分别为26025.94t、2638.57t、12016.85 t.研究表明,保护区森林生态效益显著,对于维持当地以及周边地区的生态安全具有重要意义.     

Heavy Metal-Activated Synthesis of Peptides in Chlamydomonas reinhardtii

In this study, we have addressed the capacity of the green alga Chlamydomonas reinhardtii to produce metal-binding peptides in response to stress induced by the heavy metals Cd²⁺, Hg²⁺, and Ag⁺. Cells cultured in the presence of sublethal concentrations of Cd²⁺ synthesized and accumulated oligopeptides consisting solely of glutamic acid, cysteine, and glycine in an average ratio of 3:3:1. Cadmium-induced peptides were isolated in their native form as higher molecular weight peptide-metal complexes with an apparent molecular weight of approximately 6.5 × 10³. The isolated complex bound cadmium (as evidenced by absorption spectroscopy) and sequestered (with a stoichiometry of 0.7 moles of cadmium per mole of cysteine) up to 70% of the total cadmium found in extracts of cadmium-treated cells. In Hg²⁺-treated cells, the principal thiol-containing compound induced by Hg²⁺ ions was glutathione. It is possible that glutathione functions in plant cells (as it does in animal cells) to detoxify heavy metals. Cells treated with Ag⁺ ions also synthesized a sulfur-containing component with a charge to mass ratio similar to Cd²⁺-induced peptides. But, in contrast to the results obtained using Cd²⁺ as an inducer, these molecules did not accumulate to significant levels in Ag⁺-treated cells. The presence of physiological concentrations of Cu²⁺ in the growth medium blocked the synthesis of the Ag⁺-inducible component(s) and rendered cells resistant to the toxic effects of Ag⁺, suggesting competition between Cu²⁺ and Ag⁺ ions, possibly at the level of metal uptake.